The handling and assembly of large and heavy components or machines are two of the most demanding tasks that have to be carried out in many industries. These tasks not only involve moving objects from one position to another, the weight and size of the objects determining the amount of power and space that is necessary for moving them, but often also a relatively precise positioning of the objects in particular spots or locations is required.
The correct placement of an object involves both spatial position and orientation, that is, angular position. This means that three different geometrical coordinates and three different angles have to be considered, so that the system is said to be characterized by six degrees of freedom (6-DOF). Due to the physical characteristics of the often very large and heavy objects to be handled, substantial amounts of technical skills or dexterity are often required for the correct adjustment of the six variables.
Thus, at least two different issues have to be dealt with in the context of handling and assembly: the power or force required for lifting and moving large and heavy objects, and the finesse required for precisely rotating and positioning the objects so as to, for example, position them correctly in relation to other objects or structures present in the workspace. The importance of sufficient hoist capacity and adequate positioning is clear in the case of, for example, the transport and assembly of wind turbines, airplanes, machine tools, heavy structures for buildings, heavy equipment, among others.
Many attempts have been made to design and produce manipulators capable of manipulating heavy loads. Some of the necessary capabilities that these manipulators must feature are, inter alia, control in the six degrees of freedom, precise adjustments in spatial and angular position, reduced sway during the movement of the load, efficient workspace utilization, maximum supported weight and dimensions of the load, etc.
U.S. Pat. No. 3,081,884 teaches a crane comprising a mechanism directed to solve the sway experienced by a load during its handling. This crane allegedly represents an improvement over prior art assemblies alleged to be ineffective or complex and expensive to produce. The disclosed crane incorporates a moving trolley with the anti-sway mechanism comprising a set of ropes that hold, in a suspended manner, a load lifting member with rotary means.
International Patent Application publication no. WO 97/19888 A1 sets forth another crane that allegedly constrains the sway of the load during hoisting operations. The crane includes six reeving cables suspending a lower support structure from an upper support structure wherein attachment points on each of the two structures are arranged on a trapezoidal geometry. The particular geometry of the attachment points may constrain sway movements, and position and attitude of the lower support structure may be adjusted by controlling the length of each of the six reeving cables.
A load handling apparatus with control in the six degrees of freedom is disclosed in U.S. Pat. No. 4,883,184. The apparatus, suitable for use in overhead tower or diagonal boom cranes, comprises an attachment carriage including a single take-up winch adjusting the lengths of all the six cables attached to it; a lifting platform is suspended from the carriage by means of the six cables that are secured to an attachment frame in an equidistant and coplanar arrangement configured to adjust a load imbalance in the horizontal plane. The angular adjustments of the load for the six degrees of freedom is performed by a means for rotation included below the lifting platform.
A robot capable of handling a load in six degrees of freedom is disclosed in U.S. Pat. No. 5,585,707. The robot comprises at least six reels and tendons attached to a manipulated platform and to several anchor points at several locations of the work space. Some anchor points are located at a height higher than the platform and some others at a height lower than the platform, so the platform is suspended by tendons from above and below. The platform is moved and rotated owing to the tendons supporting it, which are controlled by a computer that controls drive means for extending or retracting the tendons individually.
A modular reconfigurable manipulator including a winch support structure with a plurality of attached and independently-controlled winches is disclosed in U.S. Pat. No. 6,566,834. A support of the manipulator is suspended by cables extending from the winches that, by means of their servo axes, wind and unwind the cables so as to position the support at a selected location. Several configurations of the manipulator are possible depending on the number of cables to be used: six, seven or nine, the number of cables being set based on the physical characteristics of the manipulated platform. Even though a six-cable configuration may achieve control in the six degrees of freedom, only limited rotational stability may be provided.
U.S. Pat. No. 4,666,362 is directed to a parallel link manipulator comprising a base on which one end of a central spine and a plurality of cables are mounted, and the other end of the spine and cables are directly or indirectly connected together. Electric or hydraulic spools situated in the base of the manipulator vary the tensions in the cables by adjusting their lengths and, thus, generate a compression on the central spine. The generated compressive force pulls the spine causing the manipulator to move.
Finally, U.S. Pat. No. 7,267,240 B2 discloses a method for maintaining a position of a load on a lifting gear, in which a position of a load, which is suspended from a trolley of a lifting gear via at least four cables, is determined and a swinging motion of the load is counteracted by adjusting the length of at least one of the cables.
It would be highly convenient, for industries which during the course of their activities need to move and rotate large and/or heavy objects, to have a system or equipment that supports moving, positioning and orienting the load in a safe, controlled and precise manner, and which may be easily operated in automatic, semi-automatic or manual modes of operation.